Furnace



A mzn 23, 1935. @c; B. GRADY 1,999,046

FURNAC E Original Filed March 10, 1927, 5 Sheets-Sheet 1 INVENTOR fi ggmfas' B aafg AfioRNEYs Aprifi 23,1935. B. GRADY 139mm FURNACE.

Original Filed March 10, 1927 5 Shets-Sheet 2 1 INVENTOR C. B. GRADY A ril 23, 1935.

FURNACE s Sheets-Sheei 3 Original Filed March 10, 1927 INVENTOR riesfi; (1 1 0622 B 6/; ATTORNEYS c. B; GRADY April 23, 1935.

' FURNACE 1927 5 Sheets-Sheet 4 Original Filed March 10,

' lNvENTbR @a/Zes B. G912 BY I ATTORNEYS C. B. GRADY April 23, 1935.

, FURNACE 5 Shets-Sheet 5 Original Filed March 10, 1927 INVENTOR harlesfi (5. 21%

, ATTORNEYS treated Apr. 23, 1935 PATENT OFFICE.

ACE

Charles B. Grady, West Orange, N. 1., assignor to Metropolitan Engineering Company, a corpoiation of New York Original application March it, 1927, Serial No.1

Divided and this application May 29,

1931, Serial No. 53%.666

3 Claims.

This invention relates to furnaces and more particularly to furnaces having walls lined with heat absorbing elements and to a method of controlling or regulating the temperatures of the liquid or vapor carried by certain of the elements.

The objects of the invention are to provide a. furnace of relatively low cost capable of sustained high' rates of combustion with clear flame conditions, with a maximum exposure of fluid carrying elements to the effect of radiant heat, with eflicient circulation of the fluid carried by the elements, an arrangement equally well applicable to operation at high or low pressure, and a simple and positive control of the temperatures of the fluid carried by certain of the elements.

Although the invention is a"plicable to the distillation of oils and for kindr d purposes, it will be described. in its application to the generation of steam and control of superheated and reheated steam temperatures. In general, the control of temperature of fluid passing through the heat absorbing tubes is eflected by causing a second fluid to pass at a variable rate through ducts or tubes in contact with or adjacent to those carrying the fluid; the temperature of which is to be controlled. Thus, as a specific'example, saturated steam may be. conducted from the boiler steam drum and caused to flow downwardly through tubes exposed to the effect of radiant heat and discharged as superheated steam into a steam header. simultaneously, boiler water may be conducted from a drum and caused to flow upwardly through tubes in contact with, and preferably in the rear of .the steam tubes and discharged through headers and uptakes into the steam drum, the rate of flow of water being under valve control, the valve being located, preferably, in the uptake. As the superheat temperature tends to rise, the valve is opened to permit a more rapid flow of water whereby greater quantities of heat will be transferred to the water, and conversely, as superheat decreases the valve will be partially closed to decrease the rate of flow. The control is preferably efiected automatically and to this end the valve is operated by means. of a circuit including thermostat in the path of flow 'of the superheated steam and an indicating and regulatingthermometer. This'method of control has the advantage of simplicity, uniform temperature regardless of deposits of foreign matter on the tubev surfaces and variable furnace conditions affecting radiation and convection cur--. rents, and permitting operation at high superheat or reheat temperatures with safety. The control fluid may be air to be preheated for combustion purposes and in this case control is accomplished automatically by a circuit including the fan motor control or a damper in the air supply conduit, and a thermostat in the path of the superheated or reheated steam.

Although the invention contemplates the use of various fuels, the furnace is particularly adapt-' ed for pulverized fuel firing and comprises a combustion chamber, the inner walls of which are provided with fluid carrying elements preferably arranged vertically to provide efficient circulation, and closely to expose a maximum surface to the effect of radiant heat. In the primary combustion zone or combustion chamber proper, the fluid carrying elements are protected from the destructive effect of the flame by blocks or tiles of refractory material of high fusion temperature and high heat conductivity. These blocks are preferably made of silicon carbide (carborundum) although aluminum oxide and graphite and fire clay compositions may be employed with favorable results. The blocks are supported by the elementsor tubes and are so designed that their inner surfaces are spaced from the tube surfaces to prevent chilling of the block and darkening the inner surfaceduring operation whereby the heat transfer to the tubes is increased by re-radiation from the incandescent block. The transfer of heat is primarily by radiation but partly by conduction through that portion of the block in contact with the tube surface. The exposed surfaces of the blocks serve to reflect and re-radiate heat vto the fuel and flame stream to accelerate combustion, maintain ignition and to complete combustion of the solid constituents of the fuel, to produce very hot, clear. flame conditions in the vicinity of the burners, and in addition, to reflect and re-radiate heat to the exposed tube surfaces in the relatively cooler portion of the combustion chamber beyond the refractory lining. I

Dueto the hot, transparent combustion condition, the maximum heat transfer to the fluid carrying tubes is by radiation as the sensible heat of the gases will be relatively low; the heat of these gases is absorbed by transfer to fluid carrying tubes positioned across the path of the gases leaving the combustion chamber. In the preferred embodiment, the combustion chamber is fired downwardly and the flow of the products of combustion reverses in the lower portion of the chamber and is directed upwardly around boiler heating surfaces. During the reversal of the gas stream the solid constituents are precipitated and disposed of by suitable ash handling apparatus.

The last named boiler surfaces are preferably in the form of a boiler so designed that the flow of liquid will be downwardly from a drum, serially through bank of tubes, the last bank of which discharges the fluid into the lower ends of tubes exposed to radiant heat in the combustion chamber and connected to the same drum at their upper ends. A final heat recovery from the gases leaving the boiler may be effected by any desired type of air heater or economizer, preferably a combined air heater and economizer described in detail hereinafter and particularly in my copending application Serial No. 163,065, filed January 24, 1927.

In view of the high temperature combustion conditions and the provision made for efllcient circulation, the boiler may be operated at high pressures, such as 1350 pounds, and in view of the means for controlling superheat, the temperature of the steam may be maintained at 900- F. In view of these advantages, the steam at this pressure may be employed to operate a high pressure turbine and as exhausted therefrom may be returned to reheater tubing exposed in the combustion chamber at a lower pressure,

for example 350 pounds. The temperature of the 'sure boiler located in the same setting or one adjacent to the high p boiler furnace. This latter method is adaptable to existing low pressure power stations and in this case the existing boiler settings may be employed as low pressure steam generating units by providing suitable connecting flues to the high pressure boiler furnace.

It is to be understood that my apparatus and method is of equal utility as an oil still and in this case the fluid passing through the temperature control tubing may be oil to be re-boiled, air to 05 Fig. 5 is a front elevation showing the arrange- 'ment of the Blocks,

onlineHofFlgJ be preheated for combustion purposes 'in the still 01' water be ie mm Steam plant. the header Ill, passes through the tubes 2| of the upper bank, into the return header 22, then purposes.

Further objects and advantages of my invention will become apparent from the following description and drawings which illustrate a preferred embodiment of a my invention as to boiler furnaces and in which:

. Fig. 1 is a sectional elevation of a complete fur,-

nace, taken on linel-l of Fig. 2,

Fig. 2 is a section on line 2+2 of Fig. 1,

Fig. 3 is adetail elevation, partly diagrammatic Fig. 4 is a cross section of a portion of a wall an enlarged scale,

Fig. 6 is a detail side elevation. I Fig. '1 is a cross section of a portion'of a simple combustion chamber wall.

section, p s Fig. 9 is a cross'sectional detail modifiedforniofblock,

Fig.1) is across sectional detail showing a applied tion'. to avoid single modified form of control duct,

' 1 1 ,1115 a cross sectional'detail of a form of block,

Fig. 12 is aview taken on line fl ll of 11;

Fig. 13isacross sectional detail of a-rnodllar cross section terminating in a double hopperbottom 2, and opening laterally into a gas 1 let chamber 3, providedwith an outlet line 4 leadingtoanairheater andeconomizer I tobe described in detail hereinafter. Flues 6 and I connect'the lower portion of the chamber I with a boiler setting indicated conventionally at I. I The preferred arrangement of heat absorbing surfaces contemplates a maximum exposure-to. the effect of radiant heat and to that end, the walls of the vertical chamber l are lined with fluid carrying tubes arranged vertically on close centers. The structure of the'circulatory system is as follows: On the side wall 0, which has the greatest area, fluid carrying tubes II are connected at their lower ends to inlet header ll, and at their upper ends to collecting header l2. As the tubes arepreferably arranged as closely as their expansion will permit. the header connections are staggered and alternate tubes are bent to conform therewith as indicated, for example at it and it at both the upper and lower ends of the tubes, although the tubes maybe arranged in pairs with each pair terminating in Y connections. leading to the headers, if desired. The header I2 is connected to the drum II by tubes It which cool and support the arch ll. These tubes enter the drum at approximately water level and may be inclined if desired. Circulation through the system above described is completed through the usual down-takes, not shown, from the drum through the tubes 23 ofthe next bank etc. The tubes of each bank are properly spaced to allow a free passage of the gas. The tubes 24 of ,the lowest bank are extended inwardly and are bent upwardly and line the inner surface of the. wall 28., Tubes 26 are connected to return header 21 and are extended upwardly along the wall 28 alternating with the tubes 24, to provide a maximum of heat absorbingsurface'along this wall. Thetubesllandfltermlnateinthe'drum l,as shownat 20. f F

. Feed water is preferably first passed through economizer suchas that shown at I, and which disclosed in detail in my co-pending applica K011634105, filed January24, 192v.

arrangement, the water enters the head- 28, and passes upwardly through tubes II,

I Fig. 8 is a cross section showing a modified form of blocks adaptable to tubes of rectangular cross 33, entering the drum below water level.

In order to provide for more eflicient circulatubes of excessive length, to

facilitate tube renewals and to permit a simple installation of a combustion chamber which will be described in detail hereinafter, the tubes lining the side walls of the vertical chamber I are not continuous from top to bottom but are connected to return bends or headers on each side of the chamber. In view of the close spacing of the tubes, two headers such as 34 and 3b are positioned across each wall, the tubes being connected alternately as shown.

The simple arrangement of vertical, straight tubes and the single drum is well adapted for high pressures, but it is to be understood that the invention is not limited to the use of a single large drum. The arrangement permits wide variations in rating and may be operated at high or low ratings with uniform efficiency and uniform superheat temperatures.

Eiuperheat temperature may be controlled and maintained at any predetermined degree by the arrangement shown in detail in Figs. 2 and 3. Steam from the drum passes through the connection 35, shown on an enlarged scale in Fig. 3, and enters the inlet header it, from which it passes downwardly through the tubes ill lining the inner surface of the side wall 38 of the vertical chamber l. llhese tubes are also spaced closely and are likewise interrupted by return bends or headers 39 and Alt, in the same manner as the sidewall boiler tubing and for the same reasons. The lower ends of the superheater tubes terminate in the collecting header ti, from which the superheated steam is discharged into the main steam header d2 leading, for instance, to the turbines. As the wall structure adjacent to the tubes is carried by the tubes, the headers 36 and M are yieldingly supported as shown at and Gil. Tubes ltgare positioned preferably in the rear of and in contact with the tubes 3?, and are preferably welded thereto. The tubes it terminate at their lower ends in the inlet header it and at their upper ends in collecting header ti. In view of the relatively lower temperatures of the fluid passed through these tubes, simple return bends it may be provided to pass around the headers db and tit.

Water from the drum lid is delivered to the inlet header through down-take tit and flows upwardly through the tubes it in heat exchange relation to the tubes til and the fluid. therein, and is returned to the drum it at approximately water level through the up-talre 5d, the arrange-- ment forming a simple circulatory system.

in order to control the rate or flow of water or other liquid through tubes tit, a valve bi, is positioned, preferably in the up-talre til. This valve may be manually controlled in accordance with variations in superheat temperature but I prefer to control its position automatically. To this end, the valve ill maybe any suitable electrically operated type, connected in a circuit 52 including a thermostat 53 located preferably in the path of the discharging steam in the collecting header ti, and an indicating and regulating thermometer of any suitable type, such as that indicated conventionally at M.

The control of temperature of fluid carried by tubes exposed to heat can beaccomplished similarly by the use of air, an example being .shown in Figs l and 2, in the arrangement for .controlling .1'6-hEB-tfid steam temperature. In

this case the air used for control purposes is employed advantageously as preheated combustion air. Referring first to Fig. 2, exhaust steam from a high pressure turbine, or from the high through the tubes t6 lining the inner surface of the wall bl and is ultimately discharged into I the collecting header $8 from which it is conducted to the low pressure turbine or stage.

The control air may be forced under pressure of the blast fan t9 into branch conduit 6%, and discharged into air header ti. then passes upwardly through ducts M in the rear of tubes 5% in heat exchange relation. with the tubes and the liquid carried therein. Ducts 62 may be a simple hollow wall arrangement in which provision is made to prevent leakage of air between the tubes and into the vertical chamber, but I prefer to employ ducts such as shown in Fig. 10 which compriseschannels 62a, the side edges of which are welded to the tubes 5b as at til to form a closed duct. The air discharges from the ducts into a cross duct or air header ti, and is then led through ducts til surrounding the burners 6t. The air is finally discharged into the chamber through orifices t'l surrounding the burners tit.

The rate of flow of the air passing in heat exchange relationv with the tubes b6 may be controlled manually by means of the damper lit in the branch duct W, or if automatic control is desired, the damper tit may be operated by a. thermostat and regulating and indicating thermometer similarly to the arrangement shown in Fig. 3, or a, separate blast fan may be operated by the same means with variable speed motor control.

Additional preheated combustion air is supplied to the burner duct tall by the following apparatus. Air from the blast fan is forced under pressure through the duct tit and, under control of damper ti! passes into and through the air heater section til of the combined air heater and economizer b, from which it is discharged into the duct tt through the duct t t. Within the air heater section 6d the air passes The air transversely one or more times around the vertig .material and to provide for radiation from the inner surfaces to the tube surfaces. A portion of the blocks. preferably the side edges contact with the. tube surface and it follows that the heat transfer is accomplished partly by radiation and partly by conduction. The function of the combustion chamber is to protect the tube surfaces from the direct effect of combustion,. to reflect and radiate heat to the fuel and flame stream, to

increase flame temperature and accelerate com i I bustion, and to permitradiation to the tubes as distinguished from mere conduction through refractory walls of the prior art, all as described in detail hereinafter. v

,The structure of the blocks or'tlles and the provision made for supporting them on the tubes are shown in detail in Figs. 4\ to 14, inclusive.

. First, with reference to Figs. 4 to 7 inclusive and Fig. 10 whichdllustrate theprefeired form of block, the blocks I2 are shown with smooth sur- 5 faces I3 on the furnace side curved approximately to conform to the curvature of the tube protected thereby. The side edges 13 of the blocks are symmetrical and are extended inwardlybeyond the inner' surface 14 to provide face beyond the recesses 16 formed in' the side edges to accommodate the supporting members or clips l1. The clips 11 are thus protected from the flame and the impingement of products of combustion. The clips are preferably welded to the tubes as shown at 18, although it is to be understood that the clips may be secured to other wall members. The upper and lower edges of the block may be extended inwardly as shown "at I! and ll in Figs. 5 and 6 to prevent the entrance of foreign matter into the space 16. The blocks 12 are supported solely by the tubes and independently of one another by means of the clips 11 to avoid rapid deterioration due to weight and may be secured to the tubes before the latter are installed in the furnace. The. spaces between the fluid carrying tubes and the exterior plates 8| are filled with suitable insulating refractory such as magnesite and the entire structure supported'by the tubes by members 82 welded to the tubes as at, andsecured tothe plates 8| as In Fig. 8, Ihave shown a block 85 adaptable to ducts 86 of rectangular cross section, inthis case the blocks present a uniform flat surface 81 on the furnace side.

The block 88 shown in Fig. 9 is similar to the block 12 excepting that it isdesigned to be supported by clips welded toopposite sides of the tubes and has the advantage of an inner radiating surface, "of larger area. This type of'block need not he seemed to the tubes before erection but may be positioned after the tubes have been installed. In order that this may be facilitated, the recesses 90 have a vertical width at least twice the width of the clips SI and the lower half of the recem extends through the edge of the block, as shown in dotted lines at 92, in order that the clips may enter the recesses and the blocks;

be secured by lowering them a distance eq to the width of a clip. shapeof the c or lugs Si is such that their outer flanged enus are farther apart than the ends whichare welded to the tube. It is to accommodate this diverging shape that the recesses are cut back to the line 92 to extend clear to the back of the block, that is, to the part of the block which is remote from its furnace side. This shape of the recess permits the blocks to be secured on the tubes by a mement toward the tube from the furnace side This type of recess is shown in connectlon'with the modiflcationshown in Figs. 11 andv 12. being illustrated more clearlv in Fig. 12. In the modiflcation shown in these figures, the block as is so supported'that every third. tube 94 receives heat solely by radiation-from a flat inner surface 95. The recesses 86 are at least twice the width of .the clips II, the lower half extending through the edge of the block as at OI, so that the block may be lowered into podtion .and secured as above "described, and removed by raising anddisensasins t clips. I

In Figs. 13 and 14,.1 have shown a modification adaptable to walls lined with the so-called flntubes, the structure being substantially the same asthe arrangement shown in Figs. 11 and 12,

' the flns 09 occupy the space taken by'thetubesllandreceivehea tradiatedfrom the inner surface m of the block m. errangement is particularly advantageous in that the tubes and fins are protected from the direct effect of combustion e The operation of the apparatus is as follows:

fuel is delivered through the multiplicity of burnin the vicinity of the burners and below them due to the radiant heat reflected and radiated to the fuel and flame stream by the refractory walls of the combustion chamber 1i, and it follows that the solid constituents of the fuel are consumed very quickly and the ash is rendered incandescent. Due to e clear flame condition existing in the combus ion chamber, radiation to the blocks forming the side walls is notobstructed and a very rapid transfer of heat to the tubes is effected by radiation from the inner surfaces of the incandescent blocks, especially inview of the remarkably high heat conductivity of silicon carbide. The combustion chamber serves the additional function of radiating heat to the arch tubes l6 and t0 exposed portlonsof the side wall tubes below the combustion chamber. The heat transfer from the products of combustion to the exposed portions of the tubes is almost entirely, by radiation and it follows that as every provision been made to take advantage-of heat transfer by radiation, the sensible heat of the gases entering the outlet chamber] will be relatively low. v

Asthe gas stream reverses its direction and passes upwardly and outwardly into the chamber 3, the ash descends to the hoppers z and is ultimately discharged by suitable ash conveyors indicated at Ill.

As the temperature of the g ases leaving the outlet chamber 3 is relatively low, the convection surfaces I! are adequate and a flnal heat recovery is eflected"ifi the air heater and econot will be assumed that it is desired to main--' tain a superheat temperature of 900 F. as an example. The surface area of the'tubes should be somewhat in excess of the theoretical area necessary to obtain this temperature to provide for decreases in heat transfers at low ratings and the efl'ect of foreign matter accumulating on the surfaces. Water is permitted to flow at all times through the control tubes to absorb a portion of the'heat transferred to the superheater tubes, the rate of flow'governing the quantity of heat thus transferred. As the temperature tends to rise the valve 5| 'is=opened more widely; and

to effect this control with liquid in the same mansureturbineatfullloaditheexhauststeamatlow In this latter case the high pressure turbine will operate continuously at full load and, when peaks are to be met, they will be-carried with the low pressure turbines in the following manner: a-

very small part of the gases of combustion will be permitted to flow continuously through the fiues 6 and I to the low pressure boiler indicated at 8, the quantity being merely enough to keep the boiler steaming; then, to meet the peak loads, the quantity of fuel and air admitted to the main furnace will be increased and a greater quantity of the hot gases diverted to the'low pressure boiler. The low pressure steam is thus supplemented and the peaks carried on the low pressure units.

This is a division of my pending application No.

174,315 filed March 10, 1927, covering the temperature control organization.

Various modifications may be made in the above described apparatus and method without departing from the invention defined in the following claims.

What I claim is:

1. A furnace comprising a vertical chamber having walls composed of fluid carrying tubes, a combustion chamber within the upper portion of the vertical chamber formed of blocks of high heat conductivity and high fusion temperature, the said blocks being attached to and supported by the tubes and shielding the furnace side only of said tubes, a portion of each block being spaced from and a portion in contact with the tubes; the

said tubes being extended below the combustion chamber and exposed in the lower portion of the vertical chamber, and means for admitting fuel and air into the upper portion of the vertical chamber.

2. A block for protecting fiuid carrying tubes from the direct efiect of combustion in a furnace,

said block being formed principally of material '3. A block for protecting fluid carrying tubes from the direct eii'ect of combustion in a furnace, the block being composed of silicon carbide and having a smooth surface on one side curved to conform approximately to the tube surface, the block having extensions from its other surface along the side edges thereof, said extensions being provided with recesses for the reception of supporting members.

CHARLES B. GRADY. 

